In a known manner, a scroll refrigeration compressor comprises a sealed casing containing a stationary scroll and moving scroll following an orbital movement, each scroll including a scroll plate from which a spiral wrap extends, the spiral wraps of the stationary and moving scrolls being engaged in one another and defining variable-volume compression chambers, the compression chambers having a volume that decreases gradually from the outside, where the refrigerant gas is admitted, toward the inside.
Thus, during the relative orbital movement of the first and second scrolls, the refrigerant gas is compressed due to the decrease in the volume of the compression chambers and conveyed to the center of the first and second scrolls. The compressed refrigerant gas leaves from the central part toward a delivery chamber through a delivery conduit formed in the central part of the stationary scroll.
In order to improve the performance of such a compressor depending on the season, and more particularly depending on the demand for cold, this compressor may have a variable capacity and/or a variable compression rate.
Document U.S. Pat. No. 5,855,475 describes a scroll refrigeration compressor with a variable compression rate on the one hand comprising refrigerant fluid passage orifices formed in the scroll plate of the stationary scroll and each respectively emerging in one of the compression chambers and in the delivery chamber, and on the other hand bypass valves disposed on the surface of the scroll plate of the stationary scroll turned toward the side opposite the spiral wraps and each movable between an open position, allowing refrigerant fluid to be delivered from the corresponding compression chamber to the delivery chamber, and a closed position, preventing refrigerant fluid from being delivered from the corresponding compression chamber to the delivery chamber.
When one of the bypass valves is subjected, on the face thereof turned toward the scroll plate of the stationary scroll, to a pressure lower than the pressure in the delivery chamber, said valve is kept in its closed position and isolates the corresponding compression chamber from the delivery chamber. As a result, the compression rate of the compressor is kept at its maximum value.
When one of the bypass valves is subjected, on the face thereof turned toward the scroll plate of the stationary scroll, to a pressure higher than the pressure in the delivery chamber, said valve deforms elastically toward the open position thereof and communicates the corresponding compression chamber with the delivery chamber. This therefore results in a delivery to the delivery chamber of part of the refrigerant fluid compressed in the compression chambers in which the passage orifices emerge before that part of the refrigerant fluid reaches the center of the spiral wraps.
The presence of such passage orifices and such bypass valves makes it possible to decrease the compression rate of each compression chamber as a function of the operating conditions, and to thereby avoid over-compressing the refrigerant fluid. These arrangements must make it possible to improve the energy output of the compressor.
In order to decrease the mechanical forces exerted on the stationary scroll, and therefore on the moving scroll and the drive shaft of the moving scroll, and to decrease the heat transfer from the delivery chamber to the compression chambers through the stationary scroll, it is known to mount a separating plate on the face of the scroll plate of the stationary scroll turned toward the delivery chamber such that said delivery chamber is at least partially defined by the sealed casing of the compressor and the separating plate. The presence of such a separating plate thereby makes it possible to increase the reliability of the compressor.
Furthermore, in order to still further improve the reliability of the compressor, it is known to mount the separating plate movably with respect to the stationary scroll in a direction substantially parallel to the longitudinal axis of the compressor.
Installing bypass valves, as described in document U.S. Pat. No. 5,855,475, on the upper surface of a stationary scroll of the compressor equipped with a separating plate is difficult, or even impossible, due to the fact that access to the upper surface of the stationary scroll is hindered by the presence of the separating plate.